Gravity- and strain-induced electric fields outside metal surfaces

Abstract

The gravity-induced electric field outside a metal object supported against gravity is predominantly due to its differential compression which arises in supporting its own weight. This Dessler-Michel-Rorschach-Trammell (DMRT) field, as it has come to be known, is expected to be proportional to the strain derivative of the work function of the surface. We report the results of an experiment designed to produce this effect with mechanically applied strain rather than with gravity. In essence, we have measured the strain-induced contact-potential variation between a metal surface of known strain gradient and an unstrained capacitive probe. We describe useful solutions to the problems faced in such an experiment, which were not adequately addressed by earlier workers. A knowledge of the DMRT field is of considerable importance to experiments designed to compare the gravitational acceleration of charged particles and antiparticles inside a metallic shield. Past experiments with electrons yielded results contrary to the then-expected DMRT field. We review and partially extend the theoretical background by drawing on later results based on the jellium model of metal surfaces. Our results for Cu and Au surfaces are consistent with jellium-based calculations which imply a DMRT field that is about an order of magnitude smaller and of opposite sign to the early estimates.

Observations of the effects of adsorbates on patch potentials

“…In section 2 we briefly review our apparatus and technique, which is described in greater detail elsewhere [2,23,24]. We present our results in section 3 and a summary in section 4.…”

Using a Penning trap to weigh antiprotons

“…Precision of the Sells in the g tray tribution, is due to the crystal deformation. Recent measurements [21] have shown that the ratio between the gravity-induced electric fields and the weight of antiprotons is close to 1. A measurement of gold electrodes has yielded a ratio less than 0.18.…”

“…[the values of the magnetic field and the electric potentials can be properly chosen in order to satisfy (21)]. The effect of the force of gravity is completely negligible at typical experimental conditions for Penning traps (Zp= 1 cm, Vp =a few volts).…”

The WEAX experiment

“…In microgravity the limitation of 10 −6 is due to a cyclotron radius of 10 µm; the 10 µm resolution of the detector; and the patch effect. These limitations could be overcome in future experiments by using colder antiprotons, developing higher-resolution detectors and 5 × 10 −13 eV cm −1 DMRT Copper, copper oxides [14] 5 × 10 −14 eV cm −1 DMRT Gold, helium layer [18] 2 × 10 −10 eV cm improving techniques for reducing transverse forces in the trap, including materials with smaller patch fields and higher-order magnetic fields. At this time we see no fundamental limitation to the ultimate precision obtainable in microgravity.…”